Since, in a high performance tire for motorcycles, the rotation speed of the tire becomes high, the tire is largely affected by the centrifugal force, leading to outward expansion of the tread portion of the tire and thereby to a reduced steering stability in some cases. Therefore, a tire structure has been developed wherein a reinforcement member comprising an organic fiber or steel (spiral member) is wound around the tread portion of a tire such that it is almost in parallel with the equatorial plane of the tire.
Examples of the spiral member used in this spiral belt layer include nylon fibers, aromatic polyamides (product name: Kevlar) and steels. Among these, recent interest has focused on aromatic polyamides and steels since they do not elongate and are capable of reducing expansion of the tread portion even at a high temperature. In cases where such a spiral member is wound around the crown portion of a tire, the so called “hoop” effect (an effect which prevents, by constraining the crown portion of a tire with a spiral member, expansion of a tire due to the centrifugal force even when the tire rotates at a high speed, thereby allowing a high steering stability and durability to be exerted) can be enhanced, so that many technologies related to improvement of these spiral members have been proposed so far (e.g., Patent Documents 1 to 5).
Tires wound by these spiral members are known to be excellent in the steering stability at a high speed and exhibit a very high traction. However, in terms of the turning performance during leaning largely of a vehicle (motorbike), winding a spiral member does not cause drastic improvement in the steering stability. Therefore, consumers, and riders who participate in races sometimes demand for improvement of the grip performance during leaning largely of a motorbike.